Materials Science Forum Vol. 812

Abstract: In hot rolling mills the plastic deformation of the strip is realized at high force and plastic strain speed controlled by electro-hydraulic servo actuators. These hydraulic servo actuators - hydraulic capsules – are capable to adjust the rolling gap at great rolling force dynamically. The dynamic behaviour of the rolling mill’s AGC (automatic gap adjustment) system mainly depends on the correct operation of hydraulic actuators and servo valves. These equipments are great value, planned maintenance is essential for reliable correct operation. The maintenance includes the refurbish of damaged, worn surfaces inside the cylinder and replacement of worn out seals. In the study a laboratory hydraulic positioning system was used to examine the effect of hydraulic actuator internal leakage to dynamic behaviors of the positioning system. Because the laboratory test system is similar to the hydraulic gap adjustment system therefore the laboratory test results can be extended to the rolling mill’s Hydraulic Gap Control system.

Abstract: Hardware-in-the-Loop (HIL) test is an effective platform for developing and testing complex real-time systems and allows the engineer to examine units or equipments with greater test coverage compared to physical testing alone. Expensive and unique electro-hydraulic servo systems, which are applied in Hydraulic Gap Adjustment Systems in Hot Rolling Mills, are hard to test in different operating conditions, but a HIL test system can provide this examinations. In this paper a HIL test environment is presented which can be used to observe the dynamic behavior of the Hydraulic Gap Adjustment System.

Abstract: Master alloys are used in the metals industry to control chemical composition and to help to achieve a particular microstructure or promote growth of desired phases. This study reports on making a Al₃Nb containing aluminium (Al) - niobium (Nb) master alloy by solid-liquid reaction processing, where solid Nb particles are added to the liquid Al. Nb react with Al to form in-situ Al₃Nb. The in-situ formed Al₃Nb particles were facet and polygonal in shape. The three dimensional analysis revealed that the outer surface of the partially reacted Nb was covered with faceted Al₃Nb particles. The different nature and morphologies of the in-situ phases that were produced were determined using SEM, EDX, XRD and extraction techniques. A mechanism for the observed microstructural difference is discussed.

Abstract: Equal channel angle pressing (ECAP) of commercial purity aluminum (1050), oxygen free high conductivity copper (OFHC Cu) and high purity tin (99,99% Sn) were conducted using C processing route. The variation of microstructure, of micro-Vickers hardness and of macroscopic material parameters with number of pressings was documented up to ten passes. Tensile tests were used to evaluate post ECAP deformation response. Optical microscope was used to obtain statistical information on the microstructure developed during ECAP. The present results showed that, as it can be found in the literature, first ECAP pass has resulted in enhancement of mechanical properties. Further ECAP processing, as original observation, has resulted in slight improvement and after ~7 pressing decreasing of hardness can be observed. The true stress–strain curve for ECAP-ed specimens tested under tension showed the evolution of macroscopic material properties is similar. This behavior can be connected with the deformation microstructure of the specimen, grain deformation and fragmentation.

Abstract: The authors have investigated the influence of sintering time at 1600 °C on microstructure, shrinkage, density, surface hardness and bending strength of Al₂O₃ based ceramic composites. From the ceramic powder mixes, the specimens were compacted by uniaxial pressing and during sintering the heating gradient was 100 °C/h. The experiments have shown that at 1600°C of sintering temperature, the specimen densifications have almost finished within 5 hours, meanwhile the crystal grows processes were continued for up to 9 hours of sintering. The authors have found that the maximum values of hardness and mechanical bending strength of specimens were obtained at 5 hours of sintering and these values have slowly decreased with increasing the sintering times.

Abstract: The physical simulation is an ultimate innovative way to develop the welding processes. The paper introduces the connection between weldability and physical simulation, hot-cracking sensibility, the Gleeble 3500 thermo-mechanical physical simulator, respectively. Four kinds of materials were investigated and different kinds of physical simulation test methods were made such as, identification of the Nil-Strength Temperature (NST), hot tensile tests (on heating and on cooling parts of the welding simulation curve are also investigated). Furthermore, Heat Affected Zone (HAZ) tests are being introduced. The future approaches of the research are also exposed.

Abstract: The friction stir welding (FSW) is a dynamically developing version of the pressure welding processes. Nowadays, the knowing of the properties and the behaviour of the welded joints is an important direction of the investigations, especially under cyclic loading. The research work aimed (i) to demonstrate the behaviour of the FSW welded joints under cyclic loading conditions; (ii) to confirm the applicability of the used friction welding technology. Experiments were performed on 5754-H22 aluminium alloy and its welded joints; both high cycle fatigue (HCF) and fatigue crack propagation (FCG) tests were executed. HCF limit curves were determined based on staircase method. Statistical behaviour of the base material and the welded joints under FCG was represented by the cutting of the specimens, in other words by the using of different crack paths. FCG limit curves can be determined by own developed six step method. The investigations and their results were compared with each other and with the results can be found in the literature.

Abstract: Austenitic FeMnCr steels have high strength, high toughness and formability because of the stress-and strain-induced γ→α and γ→ε martensitic phase transformations. These are the so-called TRIP (Transformation Induced Plasticity) and TWIP (Twining induced Plasticity) effects. TWIP steels deform by both glide of individual dislocations and mechanical twinning [1]. The type and mechanism of the austenite→martensite transformation depends on the composition, deformation rate and temperature. The ratio and quantity of the resulting phases determine the properties of the product. It is known that austenitic steels can transform into α and/or ε martensite phases during plastic deformation The characteristics of the martensitic transformations induced by uni-axial tensile tests between room temperature and 200°C in a FeMnCr steel with 2,26 w% Cr content were examined. Mechanical properties as, yield stress were determined from tensile tests. Metallographic examinations, quantitative and qualitative phase analysis by X-ray diffraction were carried out on the uniformly elongated part of the samples (cross, longitudinal sections).

Abstract: Dynamic recrystallization (DRX) characteristics of an 5182 Al alloy was investigated at temperatures ranging from 673 K-773 K and constant strain rates of 0.01 s^-1, 0.1 s^-1, 1 s^-1, 10 s^-1, and 50 s^-1. The average grain size of the as-casted alloy was 160 μm and was refined to 20 μm via deformation at 773 K, 50 s^-1 to a strain level of 0.5 (40%). The true stress-strain curves were determined and divided into two main groups based on the temperatures and strain rates. The activation energy of the DRX in the examined aluminum alloys was calculated, being 175,87 kJ/mol. During the crystallization process compound phases were crystallized along the border of initial grains due to the great content of Mg, Mn and Fe. It was deduced from the metallography examination that most of the new grains formed via necklacing mechanism from the mentioned borders during the DRX.

Abstract: ISD DUNAFERR Co. Ltd., formerly named as Dunai Vasmű (Danube Ironworks), has a history of over half a century. Currently it is the only factory in Hungary that is operated by integrated steel-making technology and has a hot metal production capacity of 1.7 million tons (Figure 1). The metallurgical combine includes coke production, hot metal production, steel-making, hot and cold rolling, profiling and manufacturing of galvanized products too. Steel is produced by 2 BOFs with the capacity of 135 tons each.